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SSL decryption: refactor TLS12_PRF

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Less use of raw pointers.
This commit is contained in:
Johanna Amann 2022-01-05 15:42:48 +00:00
parent 4204615997
commit c04246bd7c
2 changed files with 37 additions and 47 deletions
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77
src/analyzer/protocol/ssl/SSL.cc
View file

@ -20,20 +20,6 @@
#include <openssl/core_names.h>
#endif
static void print_hex(std::string name, u_char* data, int len)
{
int i = 0;
printf("%s (%d): ", name.c_str(), len);
if ( len > 0 )
printf("0x%02x", data[0]);
for ( i = 1; i < len; i++ )
{
printf(" 0x%02x", data[i]);
}
printf("\n");
}
namespace zeek::analyzer::ssl
{
@ -149,21 +135,21 @@ void SSL_Analyzer::SetSecret(size_t len, const u_char* data)
secret.append((const char*)data, len);
}
void SSL_Analyzer::SetKeys(zeek::StringVal* keys)
{
SetKeys(keys->Len(), keys->Bytes());
}
void SSL_Analyzer::SetKeys(size_t len, const u_char* data)
void SSL_Analyzer::SetKeys(zeek::StringVal* nkeys)
{
keys.clear();
keys.reserve(len);
std::copy(data, data + len, std::back_inserter(keys));
keys.reserve(nkeys->Len());
std::copy(nkeys->Bytes(), nkeys->Bytes() + nkeys->Len(), std::back_inserter(keys));
}
bool SSL_Analyzer::TLS12_PRF(const std::string& secret, const std::string& label, const char* rnd1,
size_t rnd1_len, const char* rnd2, size_t rnd2_len, u_char* out,
size_t out_len)
void SSL_Analyzer::SetKeys(const std::vector<u_char> newkeys)
{
keys = newkeys;
}
std::optional<std::vector<u_char>>
SSL_Analyzer::TLS12_PRF(const std::string& secret, const std::string& label,
const std::string& rnd1, const std::string& rnd2, size_t requested_len)
{
#ifdef OPENSSL_HAVE_KDF_H
#if defined(OPENSSL_VERSION_MAJOR) && (OPENSSL_VERSION_MAJOR >= 3)
@ -178,13 +164,12 @@ bool SSL_Analyzer::TLS12_PRF(const std::string& secret, const std::string& label
#endif /* OSSL 3 */
// prepare seed: seed = label + rnd1 + rnd2
size_t seed_len = label.size() + rnd1_len + rnd2_len;
std::string seed{};
seed.reserve(seed_len);
seed.reserve(label.size() + rnd1.size() + rnd2.size());
seed.append(label);
seed.append(rnd1, rnd1_len);
seed.append(rnd2, rnd2_len);
seed.append(rnd1);
seed.append(rnd2);
#if defined(OPENSSL_VERSION_MAJOR) && (OPENSSL_VERSION_MAJOR >= 3)
// setup OSSL_PARAM array: digest, secret, seed
@ -196,20 +181,23 @@ bool SSL_Analyzer::TLS12_PRF(const std::string& secret, const std::string& label
*p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_SEED, (void*)seed.data(), seed.size());
*p = OSSL_PARAM_construct_end();
auto keybuf = std::vector<u_char>(requested_len);
// set OSSL params
if ( EVP_KDF_CTX_set_params(kctx, params) <= 0 )
goto abort;
// derive key material
if ( EVP_KDF_derive(kctx, out, out_len, NULL) <= 0 )
if ( EVP_KDF_derive(kctx, keybuf.data(), requested_len, nullptr) <= 0 )
goto abort;
EVP_KDF_CTX_free(kctx);
return true;
return keybuf;
abort:
EVP_KDF_CTX_free(kctx);
return false;
return {};
#else /* OSSL 3 */
auto keybuf = std::vector<u_char>(requested_len);
if ( EVP_PKEY_derive_init(pctx) <= 0 )
goto abort; /* Error */
// setup PKEY params: digest, secret, seed
@ -220,18 +208,18 @@ abort:
goto abort; /* Error */
if ( EVP_PKEY_CTX_add1_tls1_prf_seed(pctx, seed.data(), seed.size()) <= 0 )
goto abort; /* Error */
if ( EVP_PKEY_derive(pctx, out, &out_len) <= 0 )
if ( EVP_PKEY_derive(pctx, keybuf.data(), &requested_len) <= 0 )
goto abort; /* Error */
EVP_PKEY_CTX_free(pctx);
return true;
return keubuf;
abort:
EVP_PKEY_CTX_free(pctx);
#endif /* OSSL 3 */
#endif /* HAVE_KDF */
return false;
return {};
}
bool SSL_Analyzer::TryDecryptApplicationData(int len, const u_char* data, bool is_orig,
@ -260,19 +248,19 @@ bool SSL_Analyzer::TryDecryptApplicationData(int len, const u_char* data, bool i
if ( secret.size() != 0 && keys.size() == 0 )
{
#ifdef OPENSSL_HAVE_KDF_H
DBG_LOG(DBG_ANALYZER, "Deriving TLS keys for connection foo");
DBG_LOG(DBG_ANALYZER, "Deriving TLS keys for connection");
uint32_t ts = htonl((uint32_t)handshake_interp->gmt_unix_time());
char crand[32] = {0x00};
u_char keybuf[72];
auto c_rnd = handshake_interp->client_random();
auto s_rnd = handshake_interp->server_random();
memcpy(crand, &(ts), 4);
memcpy(crand + 4, c_rnd.data(), c_rnd.length());
auto res = TLS12_PRF(secret, "key expansion", (char*)s_rnd.data(), s_rnd.length(), crand,
sizeof(crand), keybuf, sizeof(keybuf));
std::string crand;
crand.append(reinterpret_cast<char*>(&(ts)), 4);
crand.append(reinterpret_cast<char*>(c_rnd.data()), c_rnd.length());
std::string srand(reinterpret_cast<char*>(s_rnd.data()), s_rnd.length());
// fixme - 72 should not be hardcoded
auto res = TLS12_PRF(secret, "key expansion", srand, crand, 72);
if ( ! res )
{
DBG_LOG(DBG_ANALYZER, "TLS PRF failed. Aborting.\n");
@ -280,10 +268,11 @@ bool SSL_Analyzer::TryDecryptApplicationData(int len, const u_char* data, bool i
}
// save derived keys
SetKeys(sizeof(keybuf), keybuf);
SetKeys(res.value());
#else
DBG_LOG(DBG_ANALYZER,
"Cannot derive TLS keys as Zeek was compiled without <openssl/kdf.h>");
return false;
#endif
}

7
src/analyzer/protocol/ssl/SSL.h
View file

@ -82,7 +82,7 @@ public:
*
* @param data Pointer to the key buffer as derived via TLS PRF
*/
void SetKeys(size_t len, const u_char* data);
void SetKeys(const std::vector<u_char> newkeys);
/**
* Try to decrypt TLS application data from a packet. Requires secret or keys to be set prior
@ -122,8 +122,9 @@ public:
*
* @return True, if the operation completed successfully, false otherwise
*/
bool TLS12_PRF(const std::string& secret, const std::string& label, const char* rnd1,
size_t rnd1_len, const char* rnd2, size_t rnd2_len, u_char* out, size_t out_len);
std::optional<std::vector<u_char>> TLS12_PRF(const std::string& secret,
const std::string& label, const std::string& rnd1,
const std::string& rnd2, size_t requested_len);
/**
* Forward decrypted TLS application data to child analyzers